Poison Information | The Rhubarb Compendium The Rhubarb Compendium More than you ever wanted to know about rhubarb You are here Poison Information dan - Fri, 04/09/2010 - 19:21 Rhubarb contains oxalate, which have been reported to cause poisoning when large quantities of raw or cooked leaves are ingested. The poison in rhubarb Oxalates are contained in all parts of rhubarb plants, especially in the green leaves. There is some evidence that anthraquinone glycosides are also present and may be partly responsible. It is not clear as to the exact source of poisoning from rhubarb, possibly a result of both compounds. The stalks contain low levels of oxalates, so this does not cause problems. Chemical Composition of Rhubarb 7 - 34 mg/100g During World War I rhubarb leaves were recommended as a substitute for other veggies that the war made unavailable. Apparently there were cases of acute poisoning and even some deaths. Some animals, including goats and swine, have also been poisoned by ingesting the leaves.

The biodynamic (toxicity) mechanism by which oxalic acid works is somewhat different from organic poisons and is more analogous to heavy metal poisoning. Organic poisons often work through at the biochemical level, e.g. cyanide by interfering with respiration at the cellular level, strychnine by screwing up inter-synaptic transmission. There are many molecular substances in foods which offer no nutritional benefit, and must be processed and excreted. Oxalic acid, for example, is excreted in the urine, and its crystals are commonly found in microscopic urinalysis. Too much oxalic acid in the urine will result in kidney or bladder stones. Calcium combines with oxalic acid to form the less soluble salt, calcium oxalate, which is also found in kidney stones. Plant leaves, especially rhubarb, cabbage, spinach, and beet tops, contain oxalic acid. Oxalic acid is also found in potatoes and peas. Vitamin C is metabolized to oxalic acid; it contributes to over-saturation of the urine with crystals and possibly to stone formation.

More about Oxalic acid Oxalic acid is a strong acid of the composition HOOC-COOH, which crystallizes as the ortho-acid (HO)3 CC (OH)3 . It is sometimes also called "ethane diacid". It occurs naturally in some vegetables (like rhubarb). The can also be produced by heating sodium formate and treating the resulting oxides with sulfuric acid. It can also be obtained by the action of nitric acid on sugar, or of strong alkali's on sawdust. The product is normally traded as colorless crystals with a melting point of 101.5?C, and can be dissolved in water or alcohol. Oxalic acid reduces iron compounds, and is therefore used in metal polishes, stain removers, and writing inks. When it absorbs oxygen, it is converted to the volatile carbon dioxide and to water, and it is used as a bleaching agent, in detergents, and as a mordant in dyeing processes. How toxic is rhubarb?

0.59 - 0.72 0.39 - 0.54 From an MSDS (Material Safety Data Sheet) for Oxalic acid, LD50 (LD50 is the Median Lethal Dose, which is the dose of a drug or chemical predicted to produce a lethal effect in 50 percent of the subjects to whom the dose is given) in rats is 375 mg/kg. So for a person about 145 pounds (65.7 kg) that's about 25 grams of pure oxalic acid required to cause death. Rhubarb leaves are probably around 0.5% oxalic acid, so that you would need to eat quite a large serving of leaves, like 5 kg (11 lbs), to get that 24 grams of oxalic acid. Note that it will only require a fraction of that to cause sickness.

Symptoms of Oxalic Acid Poisoning On the body body as a whole one might experience weakness, burning in the mouth, death from cardiovascular collapse; on the respiratory system - difficulty breathing; on the eyes, ears, nose, and throat - burning in the throat; one the gastrointestinal system - abdominal pain, nausea, vomiting, diarrhea; and on the nervous system - Convulsions, coma. Precautions for rhubarb gardening Compound Interest - Why Shouldn’t You Eat Rhubarb Leaves? – The Chemistry of Rhubarb Why Shouldn’t You Eat Rhubarb Leaves? – The Chemistry of Rhubarb Click to enlarge Field-grown rhubarb will shortly be coming into season and appearing in supermarkets in the UK, so it seems like a good time to take a look at the chemistry behind this odd-looking vegetable. It’s mostly used in pies and desserts, but it’s only the stalks of the plant that we eat – and there’s a reason for that. This graphic takes a look at why, and also looks at the chemical compounds that contribute to the colour and the laxative effect of rhubarb. Firstly, let’s consider the poisonous nature of rhubarb leaves.

It’s generally thought that this is due to the presence of a chemical compound called oxalic acid. This compound doesn’t just occur in rhubarb – it also occurs in lower amounts in spinach, broccoli, cauliflower, and brussels sprouts. Obviously, we eat those pretty regularly just fine; in vindication of the old adage ‘the dose makes the poison’, it’s the higher concentration in rhubarb leaves that poses the problem. Rhubarb leaves have a comparatively high oxalic acid content of around 0.5 grams per 100 grams of leaves. This is present in the form of oxalic acid, and also in the form of calcium and potassium oxalate salts, and is at a level much higher than that found in other portions of the plant such as the stem. The suggested lethal dose of oxalic acid is in the region of 15-30 grams, meaning you’d have to eat a fair few kilograms of the leaves to reach this dose, but lower doses can still cause nausea and vomiting. This was discovered to the detriment of the British government in World War I, when, due to food shortages, they advocated eating rhubarb leaves.

Of course, this led to cases of poisoning, and at least one death is reported in the literature . The only other study on a death due to oxalic acid poisoning was back in 1960, so the specifics of the mechanism of the poisoning are a little hazy. However, it’s known that, in the body, oxalic acid binds to calcium ions, producing calcium oxalate. Calcium oxalate is insoluble, and as such accrues in the kidneys as kidney stones. It’s not quite as clear as oxalic acid or oxalates being the culprit, though. Some critics have pointed out that no traces of oxalates were found in post-mortem examinations of those who supposedly died from poisoning after eating rhubarb leaves, and it’s also been suggested that there may be another, as yet unidentified chemical component in the leaves of rhubarb which contributes to their toxicity. Compounds known as anthraquinone glycosides have been suggested as potential candidates, but as yet no specific compound has been identified. This leads nicely on to a discussion of some of the other compounds found in rhubarb stems, which include anthraquinones.

They’re contributors to the colour of rhubarb, although not major contributors – that part is played by compounds called anthocyanins, common causes of colour in plants. The major anthocyanin in rhubarb is cyanidin-3-glucoside. A range of anthraquinones are also present, including emodin (orange), chrysophanol (yellow), physcion (red-orange), and rhein (red). Besides their colour contribution, these compounds and their derivatives also give rhubarb a laxative effect. The compounds of interest as far as these effects go are the sennosides, derivatives of anthraquinones. During digestion, these compounds are hydrolysed into a number of smaller molecules, including rheinanthrone. It’s rheinanthrone that is thought to be the primary compound behind rhubarb’s laxative effect. Sennosides are also found in the senna plant (hence the name), and are commonly used in laxative medications. They’re included in the World Health Organisation’s list of the essential medicines. Compounds from rhubarb have also been examined for other potential medical uses.

In particular, the anthroquinones have been researched as potential anticancer compounds, with both emodin and aloe-emodin having been shown to exhibit anti-tumour properties. Are Rhubarb Leaves Poisonous? Make a Natural Insecticide with the Leaves. Many visitors ask, " Can rhubarb leaves be composted? " It would stand to reason that if the leaves are poisonous, then adding them to compost would be a concern. However, since the oxalic acid is broken down, diluted and pH balanced quite quickly, this is not a concern. Since humans and animals do not normally ingest matter from a compost, rhubarb leaves should be able to be added safely to the compost. Go here for more information and tips for composting rhubarb leaves. Interestingly, the leaves of rhubarb can be used to make a natural insecticide. If you have a large rhubarb patch, you may be interested in making this natural insecticide using the leaves after picking your rhubarb. A Recipe for Natural Insecticide Using Rhubarb Leaves Boil 500 grams of rhubarb leaves in a few pints of water for about 20 minutes. Allow leaf mixture to cool.

Strain the liquid into a CHILD PROOF/SAFE suitable container. Add a tiny bit of dish detergent or soap flakes, (not laundry detergent). Using a spray bottle, spray on leaves to kill off bugs such as aphids and spider mites, June bugs, and fungus diseases. *NOTE - DO NOT spray this product on ANYTHING edible. Rhubarb leaves contain high amounts of oxalic acid, and are poisonous, and could cause death. If you are interested in more recipes to make simple homemade Natural Pesticides and Insecticides, Go here Here are additional pages within this website that provide helpful information about growing rhubarb in the home garden (or use the website's navigation bars): Oxalic Acid Foods - Calcium in Spinach | Dr. Weil 1 min Avoid Vegetables with Oxalic Acid? I’ve heard that spinach, as well as some other vegetables contain significant amounts of oxalic acid, which can interfere with absorption of some minerals. What you think about the oxalic acid issue? – January 28, 2008 Oxalic acid is a natural product found in spinach and some other plant foods including rhubarb.

(Levels are so high in rhubarb leaves that we don’t eat them – they’re poisonous). It imparts a sharp taste to beet greens and chard that I don’t like, especially in older leaves. As for other oxalic acid foods, concentrations of oxalic acid are pretty low in most plants and plant-based foods, but there’s enough in spinach, chard and beet greens to interfere with the absorption of the calcium these plants also contain. For example, although the calcium in spinach is 115 mg per half cup cooked, because of the interference of oxalic acid, you would have to eat more than 16 cups of raw or more than eight cups of cooked spinach to get the amount of calcium available in one cup of yogurt. However, the oxalic acid in vegetables is broken down in cooking and doesn’t interfere with the absorption of calcium present in other foods, cheese for instance, that you might eat at the same time. Calcium is available from many other food sources – in addition to yogurt, cheese and milk, it is also found in a wide variety of fortified foods including orange juice, soy milk and cereals. I certainly wouldn’t avoid spinach or other leafy greens because of the oxalic acid effect.

Spinach has a lot to offer nutritionally: it’s an excellent source of folic acid, potassium and magnesium, as well as vitamin K, carotenes, vitamin C and lutein, important for healthy eyes. As far as calcium is concerned, I recommend that women aim for a total daily calcium intake of 1,000-1,200 mg per day from all sources, including supplements of 500 to 700 mg of calcium citrate in two divided doses taken with meals. For men, I now suggest aiming for 500 mg from all sources, and unless they are getting almost no calcium from food, men should not supplement with calcium – high intake has been linked to an increased risk of prostate cancer. Andrew Weil, M.D. 3 Oxalic acid HOOCCOOHaq is found in rhubarb leaves a - CHEMISTRY - 101 3 oxalic acid hooccoohaq is found in rhubarb leaves a SCHOOL View Full Document 3. Oxalic acid, HOOCCOOH(aq), is found in rhubarb leaves. a. What is the classification of this solution? (1 mark) Acidic solution. b.

On the basis of your classification, predict the pH of a solution containing oxalic acid. (1 mark) > 7 c. On the basis of your classification, predict the result of a conductivity test for a solution containing oxalic acid. (1 mark) Weak conductor. d. Write two balanced chemical equations to show the ionization reactions that occur when oxalic acid is in aqueous solution. (2 marks) HOOCCOOH ---> H+ + -OOCCOOH -OOCCOOH ---> -OOCCOO- e. Compare the relative amount of hydronium produced by each of the ionization reactions written in question 2.d. (1 mark) The amount of H+ produced by the first ionization is greater than that produced in the second ionization. This preview has intentionally blurred sections. Sign up to view the full version. View Full Document Chemistry 20: Module 5: Lesson 3 3 Assignment 4. Sodium dihydrogen phosphate, NaH 2 PO 4 (aq), has a pH of 8.2. a. What is the classification of this solution? (1 mark) Basic solution. b.

Write two balanced chemical equations to explain the observed pH for a solution containing NaH 2 PO 4 (aq). (1 mark) NaH2PO4 ---> Na+ + HPO4- HPO4- + H2O ---> H2PO4 +OH- c. Suppose the pH was not given. Is there a different set of reactions you could have written and a different interpretation? (2 marks) This is the end of the preview. Sign up to access the rest of the document. TERM Chemistry 20: Module 5: Lesson 4 1 Assignment MODULE 5: LESSON 4 ASSIGNMENT Lesson 4 M5 L4 Rheum x hybridum, rhubarb - THE POISON GARDEN website THE POISON GARDEN website Rheum x hybridum, rhubarb Summary Rhubarb was introduced to the west as a laxative with restorative powers long before the consumption of the stalks as a dessert began but it is the leaves, deadly in 'normal' amounts, that earn it its place here. Blog Entries Meaning of the Name Rheum Some people assume there is a connection between the Rhubarb plant and rheumatism but there is not.

Rheumatism comes from Latin whereas the plant name comes from the Greek name ‘Rheon barbaron’ meaning ‘from the barbarous lands of Rha’, the Greek name for the Volga river. A cross between two species. Common Names and Synonyms How Poisonous, How Harmful? Rheum x hybridum, rhubarb Though the stalks are widely eaten as a dessert, the leaves are highly toxic. They contain oxalic acid in the form of oxalates which is widely believed to be the poison but there is evidence that these are insufficient to cause the known fatalities. There are reasons to believe that it is anthraquinone alkaloids which are to blame but the mechanisms have not been fully studied. In 1945, in the New England Journal of Medicine, Jeghers and Murphy, when discussing the issue of whether oxalates are wholly to blame for rhubarb's fatal poisonings note that 'There is a distinct paucity of reliable information on this subject in the modern literature'. They go on to encourage any physicians who encounter rhubarb poisoning to publish a case study to make a 'worth-while contribution to the medical literature'. Sixty plus years later, we are no better informed.

There appears to have been only one case study, published in 1960, and its title, 'Death of a child from oxalic acid poisoning due to eating rhubarb leaves', suggests the authors did not find anything to add to the understanding. Either the modern incidence is extremely low or the cases do not get reported as Jeghers and Murphy hoped they would. Symptoms of rhubarb poisoning are said to be, weakness, burning in the mouth and throat, breathing difficulty, pain in the eyes and stomach, nausea, vomiting, diarrhoea, seizures, red coloured urine and kidney stones. Death from eating rhubarb leaves occurs quickly and is preceded by drowsiness, possibly leading to coma, convulsions, internal bleeding and nosebleeds as coagulation is inhibited. Symptoms may begin within an hour of ingestion though in some older cases onset took much longer. Incidents A visitor to the Alnwick Garden Poison Garden reported that the family's goats had been poisoned by rhubarb leaves after the vicar threw them over the fence into the field where the goats were. Another visitor said that, when she was a child, she had fed her pet albino rabbit on rhubarb leaves and killed it.

Folklore and Facts Though stories told by visitors to the Alnwick Garden Poison Garden were always interesting to hear, they were frequently wrong. The rhubarb provides two good examples of such stories. A visitor claimed that Captain Cook had been the first person to realise the role of green vegetables in preventing scurvy which meant he had the first scurvy free vessel in the navy. Unfortunately, when other green leaves were not available he fed his crew on rhubarb leading to many deaths. In fact, Cook’s vessel suffered almost as many scurvy deaths as other vessels in the fleet in spite of his attempts to provide fresh fruit and vegetables. I can find no reference to his men being fed rhubarb leaves. Another visitor stated, as fact, that the mixture of rhubarb and pineapple is deadly. This is not so. There are numerous recipes available for rhubarb/pineapple pie. The suggestion is that the acid in pineapple combines with the small amount of oxalic acid in rhubarb stems to produce a harmful strength.

The acids in pineapples, which are not oxalic acid, could break down the cell walls of rhubarb and increase the bioavailability of the small amount of oxalic acid in the rhubarb. This could increase the acid taste but would not affect the absorption. The peak for rhubarb production in the Wakefield area came during the two world wars. Because rhubarb will take on the flavour of other substances many jams and marmalades were made with a high rhubarb content. ‘Raspberry’ jam was around 60-70% rhubarb. It is said that there was a company in Bradford making wooden raspberry seeds to put in the jam to improve its looks but I haven't been able to find any proof of this. Closer to the truth was the visitor who said rhubarb leaves had been recommended as a green vegetable during wartime shortages. I've heard this said by a number of people and they almost always say this happened in WWII. I've searched for any information on this and only found one reference.

The Canadian Biodiversity Information Facility (formerly the Canadian Poison Plants Information Service) website says that ‘ingesting rhubarb leaves has caused many fatalities, especially during World War II, when the leaves were recommended as food for a short time’. This seems to be the only reference to rhubarb leaves being used in the UK during WWII and could be a typing error because, elsewhere on the same page it says 'Human poisoning was a particular problem in World War I'. However, on the BBC’s ‘People’s War’ website a woman talks about being 12-years old in occupied France and eating rhubarb leaves as a vegetable until there was an announcement in the press that this could cause poisoning. If such poisonings did occur in France during WWII that might explain why it is a Canadian organisation that refers to it. Mrs Grieve Maud Grieve, usually referred to simply as Mrs Grieve, was a leading herbalist in the early 20th century. She used her garden in Chalfont St. Peter, Buckinghamshire in the growing and preparation of herbs. During the First World War medicinal herbs were an important substitute for the manufactured medicines which could not be obtained and Mrs Grieve set down her knowledge in a great many pamphlets.

In the 1920s, Hilda Leyel, founder of the Society of Herbalists, organised these pamphlets into a book and added American herbs, at the insistence of the publishers. ‘A Modern Herbal’ was published in 1931 and combines allusions to the old herbals alongside ‘modern’ uses of the plants and some anecdotal remedies. Mrs Grieve is a frequently used source for plant information which is unfortunate, as much of what she writes is inaccurate. Two examples will suffice. She says the Atropa belladonna berry is 'intensely sweet' whereas the taste is slightly sweet but insipid. Also, she says aconite was the poison used on Ceos when this was poison hemlock. There are, however, a number of references to problems during World War I when rhubarb leaves had been recommended as a vegetable until a number of deaths occurred and the advice was withdrawn.

Rheum x hybridum, rhubarb Mrs Grieve talks about a letter in the Gardeners Chronicle for 1846 in which the gardener of the Earl of Shrewsbury at Alton Towers, Staffordshire, told how rhubarb leaves had been used there for many years as a vegetable. Then he wrote again to correct it and say it was the leaf-stalks he meant. It is possible that this error might have been passed down leading to the misuse of the leaves. Obviously, in a printed magazine there is no way make an amendment. All that can be done is to announce a correction but, if someone only sees the original piece, they will not know about the amendment. In the electronic era, it should be easier to show corrections but that relies on people accepting that a correction is required. A few years ago, a television programme about the medicinal uses of plants included a herbalist saying that it was remarkable the rhubarb had dual properties because it had been used to treat constipation and diarrhoea.

That statement missed the key point that for a long time it was thought that the way to cure diarrhoea was to give the sufferer a 'purge' and clear them out of whatever was causing the looseness. In 1254, William of Rubruck was travelling in the Mongol empire and met an Armenian monk who claimed that root of rhubarb cut small and mixed with water would, when used in conjunction with a cross the monk had, determine whether a sick person would recover or die. If his determination indicated survival, he would give the water to the patient and the strong laxative effect would produce a remarkable physical reaction often perceived as a miracle. Site Update All the pages in the A to Z section are regularly updated. A Modern Herbal | Rhubarbs [ Top ] [ Top of Rhubarb, Turkey ] ---Part Used--- The root, scraped or rasped, halved longitudinally when very large, and then cut into transverse pieces and strung on cords to dry in the sun, the drying afterwards being completed by stove heat. It is dug in October.

Chinese or Turkey Rhubarb occurs in commerce in brownish-yellow pieces of various size, usually perforated, the holes often containing a portion of the cord used to hang the sections of the root on during drying. The outer surface is generally powdery (the bark having been removed) and shows a network of white lines. The taste is astringent and nauseous, and there is a characteristic odour. The preparations used in medicine are: the powdered root, a fluid extract, a tincture, syrup, infusion and solution. It is also employed as a principal ingredient in compound powder (Gregory's Powder) and in compound pills. [ Top ] [ Top of Rhubarb, Turkey ] ---Constituents--- The chemical constituents of Rhubarb root are not yet completely known. Recent investigations indicate that the most important constituents are a number of substances which may be divided into two groups, viz. tannoid constituents and purgative constituents, several of which have been isolated in a free state: the former are astringent and the latter laxative. Three crystalline tannoids have been extracted. The purgative constituents apparently exist in the form of an unstable crystalline substance: Rheopurgarin.

This splits up into four glucosides: two of these yield Chrysophanic acid (so named from its forming yellow crystals) and Rheochrysidin respectively. The other two glucosides have not yet been isolated, but they appear to yield Emodin and Rhein. There are also several resinous matters, one of which, Phaoretin, is purgative, and mineral compounds are also present, especially Oxalate of Calcium. The astringency of Rhubarb is due to a peculiar tannic acid (Rheo-tannic), which is soluble in water and alcohol. [ Top ] [ Top of Rhubarb, Turkey ] ---Medicinal Action and Uses--- Astringent, tonic, stomachic, aperient. In large doses, Rhubarb powder acts as a simple and safe purgative, being regarded as one of the most valuable remedies we possess, effecting a brisk, healthy purge, without clogging the bowels and producing constipation, too often consequent upon the use of the more active purgatives.

It is especially useful in cases of diarrhoea, caused by an irritating body in the intestines: the cause of irritation is removed and the after-astringent action checks the diarrhoea. The following note from The Chemist and Druggist of March 31, 1923, supports this: 'Rhubarb in Bacillary Dysentery. - An investigation was undertaken to determine the way in which rhubarb acts in this disease and which constituent was responsible for its action, one writer having stated in regard to the treatment of bacillary dysentery that no remedy in medicine has such a magical effect. (Lancet, I, 1923, 382.) A solution containing all the purgative constituents of rhubarb soluble in water (1 gr. of B.P. rhubarb extract) was allowed to act on B. dysenterial Shiga and Flexner of the bacillus No. 1 of Morgan without affecting growth in the broth tubes. Fresh undiluted ox bile has not distinct action on the bacilli, thus indicating that the therapeutic effect of rhubarb is not due to its cholagogue action.

Neither does the serum of a rabbit treated with rhubarb have any germicidal action. The nature of the therapeutic effect of rhubarb in bacillary dysentery therefore still remains obscure.' And again, September 3, 1921, in the Lancet, by Dr. R. W. Burkitt: 'In the former journal, Dr. R. W. Burkitt, of Nairobi, British East Africa, states that acute bacillary dysentery has been treated in that colony almost exclusively with powdered rhubarb for the past three years. The dose given has been 30 grains every two or three hours until the rhubarb appears in the stools. After a few doses the stools become less frequent, haemorrhage ceases, and straining and the other symptoms of acute general poisoning, which characterize the disease, rapidly disappear. In children 5 grains is given every two hours for three doses only, as, if the administration is continued longer, the drug will cure the dysentery, but produce an obstinate simple diarrhoea. In both adults and children the thirst is combated by small, frequent doses of bicarbonate of soda and citrate of potash. Dr.

Burkitt concludes: "I know of no remedy in medicine which has such a magical effect. No one who has ever used rhubarb would dream of using anything else. I hope others will try it in this dreadful tropical scourge." ' Rhubarb in small doses exhibits stomachic and tonic properties, and is employed in atonic dyspepsia, assisting digestion and creating a healthy action of the digestive organs, when in a condition of torpor and debility. The tincture is chiefly used, but the powder is equally effective and reliable. Rhubarb when chewed increases the flow of saliva. [ Top ] [ Top of Rhubarb, Turkey ] ---Preparations and Dosages--- Powdered root, 3 to 30 grains. Comp. powder, B.P. (Gregory's), 20 to 60 grains. Comp. pill, B.P., 4 to 8 grains. Solid extract, U.S.P., 4 grains. Solid extract, B.P., 2 to 8 grains. Tincture comp., B.P., 1/2 to 4 drachms. Tincture, U.S.P., 1 drachm.

Tincture aromat., U.S.P., 1/2 drachm. Fluid extract, 10 to 30 drops. Syrup, B.P., 1/2 to 2 drachms. Infusion, B.P., 1/2 to 1 OZ. Syrup, B.P. and U.S.P., 1/2 to 2 drachms. Arom. syrup, U.S.P., 2 drachms. Rheum, 1 to 4 grains. [ Top ] [ Top of Rhubarb, English ] ---Cultivation--- Rhubarb may be raised from seed, but it is better and more usual to obtain established roots. Seeds may be sown, however, in drills a foot or more apart, in the open, from March to April, and the young plants thinned out to 10 inches, transplanting them in the autumn, allowing about 4 feet every way to each plant.

Rhubarb roots may be planted at any time of the year, although mild weather in autumn or early spring is best; it should be planted on a clear, open spot, on good soil, which should be well trenched 3 feet deep, and before planting, a good substance of rotten manure should be worked into the soil. When the plants are to be increased, it is merely necessary to take up large roots and divide them with a spade: every piece that has a crown to it will grow. Fresh plantations are generally made in February or March, but Rhubarb may still be divided early in May. To ensure fine rhubarb for table use, a large dressing of well-rotted manure should be dug in about the roots as soon as the last of the leaves have been pulled. It is not right to wait until the winter, before the plants are dressed. Old roots ought to be divided and replanted every fourth or fifth year, when the plants are grown for the use of the stems. If Rhubarb be forced on the ground where it grows, nothing more is required than to cover with large pots, half casks, or boxes, round and over which should be placed plenty of stable manure.

Roots forced in greenhouse or in frames do not need to have the light excluded from them. Such roots, however, require dividing and replanting in the spring out of doors. [ Top ] [ Top of Rhubarb, English ] ---Part Used Medicinally and Preparation--- The roots of English Rhubarb are generally taken from plants from four years old and upwards. They are dug up in October, washed thoroughly and the fibres taken away. The bark of English Rhubarb is not usually removed. The roots of both R. Officinale and R. Rhaponticum are much smaller than those of the Chinese Rhubarb and are easily distinguished by their distinctly radiate structure. They are also more shrunken, more or less distinctly pink in colour, and have a diffuse circle of isolated star-spots on the transverse section. The roots of R. officinale cultivated in England resemble Chinese Rhubarb, but are more spongy, and shrink and wrinkle as they dry, and are softer to cut.

They have a less rich colour than the Chinese, and have no network of white lines on the outer surface, the dark red and white lines usually running parallel to each other and the star-spots being less developed, fewer and more scattered. The English Rhubarb from R. Rhaponticum shows red veins, that of R. officinale is usually in larger pieces and has blackish veins. The root is used as a drug in powdered form. [ Top ] [ Top of Rhubarb, English ] ---Constituents--- Root. The constituents of R. officinale are similar to those of Chinese Rhubarb. Rhapontic or Garden Rhubarb contains no emodine, rhein or rhabarberine, but has in it a crystalline body, rhaponticin. Stem and Leaves of R. Rhaponticum. Potassium oxalate is present in quantity in Rhubarb leaf-stems, and certain persons who are constitutionally susceptible to salts of oxalic acid, show symptoms of irritant poisoning after eating rhubarb stewed in the ordinary manner.

Many people of a gouty tendency do well to avoid it, and those subject to urinary irritation should take it very sparingly or not at all. Rhubarb stems did not come into general use as a substitute for fruit till about 100 years ago. We hear of a pioneer grower, Joseph Myatt, of Deptford, sending, in 1810, five bunches of Rhubarb to the Borough Market and only being able to dispose of three. But he persevered in his efforts to make a market for Rhubarb, raised improved varieties, and a few years after, Rhubarb had become established in public favour as a culinary plant. It was, however, soon realized that the use of Rhubarb as food was sometimes attended with some risk to health. Lindley, in his Vegetable Kingdom, 1846, remarks that oxalic acid exists in both Docks and Rhubarb, and that the latter contains also an abundance of nitric and malic acid, and goes on to say that whilst these give an agreeable taste to the Rhubarb when cooked, he considers them illsuited to the digestion of some persons.

The Penny Cyclopaedia, 1841, warned persons subject to calculous complaints against eating Rhubarb stalks, owing to the presence of oxalic acid, stating that 'the formation of oxalate of lime, or mulberry calculus, may be the consequence of indulgence.' The chemical constituents of Rhubarb leaves were till recently not fully ascertained, but the analysis has lately been undertaken under orders from the Home Office, in consequence of fatal and injurious effects having resulted from eating the leaves cooked as spinach. The report of the official analyist states that the leaves contain some 0.3 per cent oxalates of potassium and calcium oxalates. It is possible that the recent cases of poisoning occurred in subjects specially susceptible to oxalic poisoning, as there are also many cases reported of no harm ensuing from a use of Rhubarb leaves as a vegetable. In Maunders' Treasury of Botany Rhubarb leaves are mentioned as a pot-herb.

Green (Universal Herbal, 1832) says: 'The leaves are also used by the French in their soups, to which they impart an agreeable acidity, like that of Sorrel.' Reference has recently been made in the press to a letter which appeared in the Gardeners' Chronicle for 1846, in which the gardener of the Earl of Shrewsbury at Alton Towers, Staffordshire, told how rhubarb leaves had been used there for many years as a vegetable. He also mentioned that the flower of the plant (before the leaves expanded) could be used like broccoli. A subsequent note by him makes it clear, however, that the leaf-stems were meant, for he then says: 'I have no experience in the eating of the leaves and think them nauseous to the taste and unpleasant to the smell.... I tasted them boiled and they did not appear to me to have one redeeming feature....' The flower of the plant, when in bud form, has been eaten as a pleasant substitute for broccoli; when cooked au gratin, with white sauce over it, the cheese quite obviates any bitterness of taste.

Further reference to the Gardeners' Chronicle, of 1847, shows records of the varying results of eating the young inflorescence, producing no ill-effects in some cases and serious illness in others, and a case is recorded of severe sickness attacking a whole family after partaking of the leaves boiled as a vegetable. In 1853 we find the question again raised. In 1872 we hear of deaths from eating the leaves in America, and in 1899 we find a revival of interest in Rhubarb leaves as a vegetable, quite opposite opinions being expressed in a correspondence in the gardening papers. In 1901 we hear of a man dying after eating stewed Rhubarb leaves, the verdict at the inquest being: 'Accidental death, caused by eating rhubarb-leaves.' It was stated then that the leaves were used as a vegetable in parts of Hampshire. The British Medical Journal in December, 1910, mentions several cases of rhubarb poisoning. The leaves are sometimes made use of in the fabrication of fictitious cigars and tobacco.

The shape of the hairs, however, as seen under a microscope, can enable the observer to detect the presence or absence of tobacco, but it is not so easy to determine the source of the fraudulent admixtures. It is possible that the chemical composition of Rhubarb varies to some extent according to the variety and the soil on which it is grown. It has been stated that the amount of water present is less when the plants are grown on poor soil, while the acid principle is more abundant. As regards the method of cooking, the British Medical Journal points out that hard water would precipitate the oxalate, while a soft water might leave it in the form of soluble oxalate, more readily assimilated into the systems of those susceptible to this kind of poisoning. In a recent case that terminated fatally, the leaves were well washed, drained, cut up and put into boiling water, in an iron saucepan, for 20 minutes. A little salt and kitchen soda were added, but nothing else. Being acid, the leaves should, of course, not be cooked in a copper vessel.

---Medicinal Action and Uses--- Though the English Rhubarb root is milder as a purgative, it is more astringent, and has been considered a better stomachic than the foreign. It is specially useful in infantile stomach troubles and looseness of the bowels. In fairly large doses it acts as a laxative. Dose of powdered root, 5 to 60 grains. The dose is entirely individual, 12 grains acting on some persons, as much as 20 on others of the same age. It has been held that 20 grains of the seed are equal to 30 of the root, as regards purgative power. The properties of the seeds are similar to those of the root. A decoction of the seeds is supposed not only to ease pains in the stomach, but to strengthen it by increasing the appetite. A strong decoction of the root has been employed as a good w ash for scrofulous sores. If a portion of the root be infused in water, and when strained a few grains of salt of tartar be added, a very beautiful red tincture results, which might prove valuable for the purposes of a dye.

Culpepper says of Rhubarb: 'If your body be anything strong, you may take 2 drams of it at a time being sliced thin and steeped all night in white wine, in the morning strain it out and drink the white wine; it purges but gently, it leaves a binding quality behind it, therefore dried a little by the fire and beaten into powder, it is usually given in Fluxes.'

Question: What acid is found in rhubarb leaves?
Answer: OXALIC ACID